Optical signals are increasingly used in communication networks to carry data. These communication networks use optoelectronic modules (such as optical transmitters, receivers, and transceivers) to transmit and receive optical signals.
In an optoelectronic module, a light source (such as a laser in a transmitter or an optical fiber in a receiver) must be accurately aligned with a lens and a target (such as an optical fiber in a transmitter or a photodiode in a receiver) in order for the optical signals to be properly routed through the communication network.
FIG. 1 shows a diagram of a conventional optical path in an optoelectronic transmitter 11. The optoelectronic transmitter 11 includes a laser 13, coupling optics 15, and an optical fiber 17. The coupling optics 15 receives light from the laser 13 and focuses it onto the optical fiber 17. The coupling optics 15 is a single unit having a first lens surface 19 and a second lens surface 21. Positioning the coupling optics is difficult because the first lens surface 19 must be aligned with laser 13 while simultaneously aligning the second lens surface 21 with the optical fiber 17.
Consequently, active alignment is needed to carefully place each component such that the light from the light source will be focused exactly on the target. For example, during active alignment of the optoelectronic transmitter 11, the laser 13 is switched on while the positions of the coupling optics 15 and optical fiber 17 are adjusted. The power of the optical signal received by the optical fiber 17 is measured. The laser 13, coupling optics 15, and optical fiber 17 are considered to be at an optimal alignment when the optical power measured is at a maximum level. At this point, the positions of the laser 13, coupling optics 15, and optical fiber 17 are fixed in place with respect to one another.
Active alignment is time consuming and expensive. It requires precision mechanical equipment to achieve the alignment, as well as optoelectronic test equipment to power and monitor the system.